The present invention relates to self-processing type photographic film units. More particularly, the invention relates to an improved self-processing type photographic film unit having a trap structure for collecting at a predetermined position in the unit surplus processing solution used in developing the unit.
The term "self-processing type photographic film unit", hereinafter referred to merely as "a unit" when applicable, as used herein refers to so-called "instant print film" which is manufactured by Polaroid Co. or Eastman Kodak Co. for instance.
There are currently available various types of units employing different layer constructions and developing methods. However, they are alike in their basic construction. A prior art unit, as shown in FIG. 1, includes two main flexible sheets, namely, a first sheet member 11 including an image receiving layer and a second sheet member 12 provided to facilitate in uniformly distributing processing solution to a predetermined thickness. The two sheet members 11 and 12 are bonded together by a bonding member 13, such as an intermediate sheet or tape, in such a manner that the sheet member 12 is above the sheet member 11. When assembled, the two sheets 11 and 12 form a container structure 16 along the front edge of the unit and a trap structure 17 along the rear edge. The container structure 16 holds processing solution. Upon application of external pressure, a predetermined part or parts of the container structure 16 are opened so that the processing solution held therein is spread over a processing liquid spreading region 15 which is defined between the two sheet members 11 and 12. The trap structure 17 operates to catch any surplus of the processing solution thus spread.
To develop the unit 10 after exposure, the entire unit 10 is squeezed beginning with the front edge. Therefore, first the container structure 16 is opened so that the processing solution is discharged into the processing solution spreading region 15 between the sheet members 11 and 12 gradually spreading the pressing solution towards the rear edge of the unit 10.
The processing solution discharged into the processing solution spreading region 15 together with a small quantity of gas from the spreading region 15 is moved towards the rear edge of the unit 10 and surplus processing solution and the gas are pushed into the trap structure. In this way, the spreading of the processing solution is accomplished.
In this operation, it is necessary to discharge the gas which was pushed into the trap structure 17 outside with the movement of the processing liquid; otherwise not only the spreading and movement of the processing liquid would not be effected smoothly but also the gas would remain in the spreading region 15 or would be moved back to the spreading region from the trap structure 17 thus causing an irregularly developed picture.
In order to overcome this difficulty, a variety of techniques have been proposed in the art to improve the gas discharging mechanism of the trap structure 17. In one example of such an improved mechanism, as disclosed in U.S. Pat. Nos. 2,262,460, 3,615,540 and 3,619,193, holes or slits are formed in the trap cover member. These holes or slits are so small that they cannot be visually detected. The holes or slits resist the passage of the viscous processing liquid but permit the passage of the gas.
In another technique, as disclosed in U.S. Pat. No. 3,589,904, the two sheet members are bonded together through the bonding member except for in a small region of the bonding member so that the gas can be discharged through the small region.
In accordance with another technique, as disclosed in U.S. Pat. No. 2,627,460, the rear edge of the film unit is made of a porous material such as a porous polymer film or a fibrous material so as to permit the passage of the gas with minimum resistance and to effectively stop the passage of the viscous processing solution.
Another conventional technique has been disclosed in Japanese Laid-Open Patent Application No. 11027/1977 which, as shown in FIG. 2, provides a trap structure 27 having a gas discharging mechanism. In this conventional trap structure, the rear edge portion of a bonding member 13 which bonds first and second sheet members 11 and 12 together extends past the rear edge of the two sheet members 11 and 12 and is then folded over the upper surface of the second sheet member 12 thereby forming a trap cover member 21 in the form of a pouch having a hollow interior. The trap cover member 21 has a number of gas discharge through-holes 22 in a line formed in the upper surface. The second sheet member 12 has a cut 23 at the rear end portion thereof in the hollow interior of the trap cover member 21. A porous spacer member 24 is provided in the hollow interior with part of the spacer member 24 fitted into the cut 23. A layer 25 for preventing permeation of the processing solution is provided on the upper surface of the spacer member 24 or between the trap cover member 21 and the spacer member 24. With the trap structure 27 thus constructed, the surplus processing solution is caught in the small pores of the porous spacer member 24 and only the gas is allowed to reach the gas discharging holes 22.
However, it has been found that, with the trap structure of the conventional unit described above, it is difficult to completely prevent leakage of the surplus processing solution and to improve the gas permeability, depending on the conditions of use of the camera or the storage conditions of the unit.
The inventor has conducted intensive research and analysis to determine the factors which affect the leakage of surplus processing solution and which cause unsatisfactory gas permeation and, as a result, has found the following:
(1) A cause of surplus processing solution leakage is the increased quantity of surplus processing solution leakage pushed into the trap structure resulting upon increased temperature and humidity or mechanical errors in the camera. Especially when the unit is processed under conditions of a temperature of 40.degree. C. or more and a humidity of 90% RH or more, surplus processing solution tends to leak.
(2) Another cause is that, after the unit has been exposed, the trap structure of the unit can be carelessly pressurized by the user. This problem has been solved to an extent by the provision of a unit according to the above-described Japanese Laid-Open Patent Application No. 11027/1977. However, if this problem co-exists with the problem of paragraph (1), surplus processing solution will still leak.
(3) The cause for the unsatisfactory gas permeability is that the gas flow path in the trap structure can become blocked by undesirable adhesion which occurs between the upper and lower inner walls of the trap cover member or between the inner walls and the surface of the layer which resists passage of the processing solution.
In view of the above-described causes, the inventor has conducted studies and experiments and from them accomplished the present invention.
Accordingly, a first object of the invention is to provide a unit in which all of the above-described difficulties accompanying a conventional unit have been eliminated.
A second object of the invention is to provide a unit in which, without greatly altering the basic arrangement of the conventional unit and utilizing the basic conventional processing system, the processing solution is uniformly spread, surplus processing solution is completely caught, and trapped gas is smoothly and effectively discharged.